1. Field of the Invention
The present invention relates to an ink-jet printing apparatus and an ink-jet printing method for printing on a printing medium by using a printing head capable of ejecting ink.
2. Description of the Related Art
The ink-jet system performs printing by projecting ink droplets (printing liquid droplets) from nozzles of the printing head onto the printing medium.
The serial printer of such a construction has a problem that when the surface of a printing medium is rubbed immediately after an image has been printed, the printed image may be spoiled or the surface of the printing medium may be smeared. Further, when a plurality of color inks are used for printing, different color inks may flow over a boundary into each other's area (bleeding), degrading an image quality. To deal with these problems, an ink-jet printing apparatus was proposed which uses inks containing ultraviolet-curing agents and radiates ultraviolet light on the printed surface immediately after printing to improve a quick drying performance of the printed surface (Japanese Patent Application Laid-Open No. 60-132767 (1985) and U.S. Pat. No. 6,092,890).
The Japanese Patent Application Laid-Open No. 60-132767 (1985) (hereinafter referred to as a “first prior art”) is intended to provide a highly reliable ink-jet printer that can prevent ink clogging and an ink-jet printer that can prevent the printed surface from getting smeared with ink even when touched by a hand immediately after printing. More specifically, the ink-jet printer uses ultraviolet-curable inks as inks to be ejected from the ink-jet printing head and radiates ultraviolet light after the inks have landed on the printing medium for their drying and fixing. Ultraviolet lamps are installed at both ends of the printing head. When the printing head is moving to the right, the left side ultraviolet lamp is used to fix the ink. When the printing head is moving to the left, the right side ultraviolet lamp is used for ink fixing. The first prior art also describes another example construction in which an ultraviolet lamp with its length corresponding to the width of the printing medium is fixedly installed at a position on the printing medium discharge side with respect to the printing head so as to fix the inks through ultraviolet radiation.
U.S. Pat. No. 6,092,890 (hereinafter referred to as a “second prior art”) is intended to provide an image forming apparatus capable of forming on an image carrier a durable image free of bleeding. In more concrete terms, the apparatus has an printing head for ejecting ultraviolet-curable inks and an ultraviolet radiation unit connected to the printing head. The image carrier, the ink-jet head and the ultraviolet radiation unit are movable relative to each other. An input digital image is formed on the image carrier by scanning a plurality of printing heads over the image carrier, with the ultraviolet radiation unit shining in each scan ultraviolet light that solidifies the inks on the image carrier.
These conventional apparatus, however, do not consider a problem of ink mist produced during printing, i.e., the adverse effects that fine ink droplets (other than the intended main ink droplets) floating over the printing medium have on the print quality. The generated mist flows rearward as the printing head scans. Thus, when the ultraviolet light is radiated immediately after printing as in the conventional apparatus, the mist also is subjected to the ultraviolet light and becomes solidified. As a result, the solidified fine ink particles are scattered over the printed surface of the printing medium, degrading the quality of the printed image. Further, a part of the mist flies to the ultraviolet radiation unit where it may be hardened and accumulate. In that case, the ultraviolet light emitted from the ultraviolet radiation unit may weaken in intensity. Further, when an ultraviolet lamp with its length corresponding to the width of the printing medium is used, as in the second example of the first prior art, the cost increases. In addition, because it takes time for the printed ink to become fixed, when a plurality of color inks are used for printing in particular, the ink bleeding at a boundary between different color ink areas adversely affects the image.